Earth is entering a stream of debris from Comet Swift-Tuttle, source of the annual Perseid meteor shower


The shower is expected to peak on the nights of August 12-13 with as many as 100 Perseids per hour. Even now NASA’s all-sky network of meteor cameras is detecting a fair number of Perseid fireballs. “We have seen more than 78 fireballs since July 27th,” reports Bill Cooke of NASA’s Meteoroid Environment Office. He prepared this plot showing the orbits of all the fireballs so far

The green ellipses trace the orbits of meteoroids, which have disintegrated brightly in Earth’s atmosphere. The orbits of the meteoroids are a good match to the orbit of the parent comet, shown in purple.

“Comet debris particles a few cm wide are hitting the atmosphere with an average speed of 59.6 km/s (133,350 mph),” continues Cooke. “The average magnitude of the resulting fireballs is -3.7, about as bright as Venus.”

Cooke and colleagues have been monitoring fireball activity for years, and they have found that the Perseids produce more fireballs than any other annual shower. Check out their data.

“Comet Swift-Tuttle has a huge nucleus–about 26 km in diameter,” notes Cooke. “Most other comets are much smaller, with nuclei only a few kilometers across. As a result, Comet Swift-Tuttle produces a large number of meteoroids, many of which are hefty enough to produce fireballs.”

More fireballs are in the offing as Earth moves deeper into the debris stream of Comet Swift-Tuttle. Stay tuned on

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